The present invention relates to a die cast nozzle and a method for operating a die cast nozzle for use in a die cast hot chamber system for molten metal with at least one melt channel in a channel carrier that can be connected to a melt distributor, wherein the melt channel passes over into a heating zone and subsequently into a nozzle tip, where a sprue section is connected. The die cast nozzle is intended for the formation of a plug in the sprue section made of solidified melting that interrupts the melt flow and can be re-fused entirely.
The sprue as a by-product of the casting that solidifies in the channels between the die cast nozzle and the casting mold in conventional die casting procedures and connects the cast parts after demolding in an ultimately undesirable manner, brings with it additional material input that is usually between 40 and 100 percent of the cast part's weight. Even if the sprue is melted down again for material recycling, this is connected with energy and quality losses due to emerging slag and oxide shares. The die cast without sprue avoids these drawbacks.
For die cast without sprue it is necessary to bring up the melting in liquid form from the crucible to the mold either for every cast and then bring it back, which results in loss of quality however, or at the least in loss of time, or as an alternative to this to hold the melting in liquid form up to the sprue of the mold. The latter is done in the hot chamber process, where all channels up to the sprue are heated in a way that the melting remains liquid and is at best prevented from reflowing to the crucible at the same time.
Reflow into the crucible can be prevented by valves, but also in a particularly advantageous manner by a plug of solidified melting that seals the sprue opening in the die cast nozzle.
Devices and methods for die cast or injection molding without sprue with the formation of a plug of solidified melting that seals a sprue section against melt flow and that can be re-fused again are known in the state of the art. Such devices and methods are particularly described for injection molding of plastics, but occasionally for die casting of non-ferrous metals.
The publication EP 1201335 A1 describes a hot chamber process for non-ferrous metals with a heated sprue die, the sprue section, where a reflowing of the melting into the channels and the crucible is prevented by a plug in the unheated nozzle die. The sprue die is heated externally. The plug comes loose from the wall of the sprue die when heated and is ejected from the nozzle die by the melting injected during the next molding procedure.
An intake room for the plug is required, so that the solid plug is not immediately injected into the mold. However, the flow of the melting during injection is obstructed by this. As this enters the mold with a velocity of 50 to 100 meters per second, the mold could be damaged by a loose plug that is carried by the melting. A controlled and complete re-fusing of the plug is not possible. Even if this was attempted, very long cycle times that would impair productivity would be required due to the sluggish external heating.
DE 33 35 280 A1 describes an electrically-operated heating element for heating molten metal in a hot chamber tool, whereby not only the die but the largest portion of the melting could be heated. Similar heating elements are extensively known in the state of the art for use within die cast nozzles for plastic melting. However, they perform a different task here. Because due to poor thermal conductivity and increased sensibility against local overheating, it comes down to ensuring an even temperature of the heating element when die casting plastics that is not too much in excess of the melting temperature. For use in metal die casting however, such heating elements can rarely be found even in literature.
The abovementioned publication DE 33 35 280 A1 has set itself to use such a one heating element in metal die casting. To do this, a heating element formed as a metal core is encompassed by an insulation layer that insulates the heating element against the metal outer sheath that is preferably made of construction steel.
The drawback here is that the heating rod has high thermal inertia due to the metal core, the insulation between heating and outer sheath as well as the metal outer sheath itself. It is possible to keep the melting in the die cast nozzle evenly warm however, but dynamic operation in time with the casting process is impossible. In particular it is not possible to seal the sprue section after every casting process using solidified melting and then re-fuse it afterwards, but the melting can only be permanently maintained in liquid form. Also, the metal outer sheath is exposed to the aggressive melting that would form an alloy with it in the interaction of high temperatures in the contact area between melting and outer sheath and that would corrode it in a short time.
The publication DE 10 2005 042 867 A1 also describes a die cast nozzle that is suitable for forming a plug that seals the sprue. However, the external heating on the nozzle leads to high thermal inertia, since the entire nozzle tip must be warmed for re-fusing and cooled down for the solidification of the plug. Due to inertia, long cycle times and as a consequence, low productivity or only partial melting of the plug ensues, that is then ejected into the mold. The abovementioned advantages of the specified documents of the state of the art bring along that the use of methods with solidifying plugs in the sprue section is not made. Low productivity and wear issues do not allow for use in practice so far.
This results in the task of providing a die cast nozzle with a heating cartridge and a method for its use, wherein the die cast nozzle should have thermal dynamics at high service life that enables operation in time with the casting process in a manner that the melting solidifies at least in a section of the die cast nozzle after every casting process insofar as a temporary seal of the nozzle ensues and emission or reflow of the melting is prevented.